1. Field of the Invention
The present invention relates to a connection pin and more particularly to a connection pin for use with a main distributing frame (referred to as MDF hereinafter).
2. Description of Related Art
An automatic MDF apparatus is an apparatus which is provided between subscribers and the switching system and automatically performs the installation, move, and removal of a telephone line. The automatic MDF apparatus includes a matrix board which accommodates a plurality of lines on the subscriber side and a plurality of lines on the switching system side, connection pins which are inserted into the through-holes in the matrix board to connect between the subscriber's lines and the switching system's lines, and a robot which manipulates the connection pins.
The matrix board has a layer of parallel pattern traces on the subscriber side and a layer of parallel pattern traces on the switching system side, the layers being in different parallel planes, insulated from each other. The layers are arranged so that the parallel pattern traces of one layer are perpendicular to those of the other. The through-holes are formed which extend through the pattern traces of the two layers at the intersections of the pattern traces.
The through-holes are not electrically conductive and therefore the patterns on the subscriber side are electrically isolated from those on the switching system side. Upon insertion of the connection pin having an electrical conductor or conductors into the through-hole, the conductor of the connection pin establishes electrical connection between the subscriber's pattern trace and the switching system's pattern trace, thereby making a line connection between the subscriber's line and the switching system's line.
A telephone line requires a pair of lines, i.e., a sending line and a receiving line. Thus, the matrix board includes four layers of patterns, i.e., a pair of wires for subscriber side and a pair of wires for the switching system side. The connection pin includes a pair of conductors so that an insertion of the connection pin makes a pair of connections simultaneously. A prior art connection pin is made of a resilient and electrically conductive material and has a diameter slightly larger than that of the through-hole in the matrix board. The prior art connection pin is press-fitted into the through-hole so that the connection pin is in pressure contact with the through-hole.
More specifically, the connection pin is a hollow cylinder with a longitudinal slit, formed therein. The connection pin has a diameter slightly larger than that of the through-hole. When the connection pin is forcibly inserted into the through-hole, the connection pin is resiliently deformed in such a way that the slit becomes narrower. This deformation of the connection pin allows the outer diameter of the connection pin to be adjusted to the inner diameter of the through-hole.
Another example of a connection pin includes a conductor in the form of wire springs having resilience and electrical conductivity. The wire springs are mounted to the connection pin to extend outwardly thereof so that the spring-to-spring distance is slightly longer than the inner diameter of the through-hole. As the connection pin is inserted into the through-hole, the springs are deformed toward each other due to pressures exerted by the inner wall of the through-hole so that the connection pin moves into pressure contact with the through-hole.
Recently, high density package and miniaturization of the switching system have become increasing necessary, and therefore such necessity has placed demands on the miniaturization of connection pins. However, the aforementioned prior art connection pin does not lend itself to miniaturization since the prior art connection pin is difficult to manufacture if it is to be miniaturized.
For example, the hollow cylinder type connection pin having a slit formed therein is manufactured by folding a metal sheet. It is difficult to shape the material into a hollow cylinder with a uniform width of slit, therefore it is difficult to provide a desired contact pressure against the inner wall of the through-hole. A poorly bent cylinder can cause the conductor to be caught by the matrix board when inserted into the through-hole, leading to damages and troubles of connection.
The wire spring type connection pins are also difficult to manufacture and can result in damages and troubles when the connection pins are inserted into or pulled out of the through-hole.